The present invention relates to a positioning device using a signal from a positioning satellite, a method of controlling a positioning device, a positioning control program, and a computer-readable recording medium having a positioning control program recorded thereon.
A positioning system has been used which locates the present position of a GPS receiver utilizing a global positioning system (GPS) (satellite navigation system) or the like.
The GPS receiver receives signals from three or more GPS satellites, and calculates the distance between each GPS satellite and the GPS receiver (hereinafter called “pseudo-range”) from the difference between the time at which the signal is transmitted from each GPS satellite and the time at which the signal reaches the GPS receiver (hereinafter called “delay time”), for example. The GPS receiver calculates (locates) the present position using the pseudo-range and satellite orbital information of each GPS satellite contained in the signal received from each GPS satellite.
However, when the signal from the GPS satellite reaches the GPS receiver after being reflected by a building or the like, or the signal strength is weak, or the dilution of precision (DOP) of the GPS satellite in the sky is low, the located position may significantly differ from the true position, whereby the accuracy of the located position may deteriorate.
On the other hand, technology has been proposed which calculates the present expected position (hereinafter called “expected position”) from the velocity vector and the elapsed time based on the preceding position, and averages the expected position and the present located position (e.g. JP-A-8-68651 (e.g. FIG. 5)).
However, the GPS satellite moves in the satellite orbit even when the GPS receiver stands still, and the reception state of the satellite signal changes from moment to moment. Therefore, the velocity indicated by the velocity vector does not necessarily become zero.
According to the above technology, when the elapsed time is 10 seconds, the expected position differs from the preceding position at a distance corresponding to 10 seconds even when the GPS receiver stands still. As a result, the accuracy of the position after averaging deteriorates, whereby the output position may differ from the true position.
According to the above technology, when the GPS receiver stands still, the expected position cumulatively differs from the preceding position as the time elapsed from the preceding positioning increases, whereby the output position differs from the true position.
Moreover, the accuracy of the velocity vector calculated based on the signal from the GPS satellite deteriorates depending on the signal reception state and the like.